[GHC] #8029: batch-mode recompilation checking sometimes fails

[GHC]

#8029: batch-mode recompilation checking sometimes fails
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        Reporter:  jwlato    |            Owner:
            Type:  bug       |           Status:  new
        Priority:  normal    |        Milestone:
       Component:  Compiler  |          Version:  7.6.3
      Resolution:            |         Keywords:  recompilation, batch-mode
Operating System:            |     Architecture:  Unknown/Multiple
  Unknown/Multiple           |       Difficulty:  Unknown
 Type of failure:            |       Blocked By:
  None/Unknown               |  Related Tickets:
       Test Case:            |
        Blocking:            |
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Comment (by jwlato):

 I think adding the package information to the error message is probably a
 good idea in general, although it won't help in this case, because
 ```Data.List.foo``` is from the home package although the user is
 expecting Data.List to be imported from base.  But I still think it would
 be useful and should happen anyway.

 The use case I have is with ghc-parmake, which calls ```ghc -M```, and
 then issues appropriate calls to ```ghc -c```.  We don't want to clean all
 the intermediate .hi/.o files, because that obviates the usage of make
 dependencies.  ghc-parmake could probably call ```ghc -c --make```, which
 would do the right thing at the cost of making each call to ghc take
 marginally longer.  Or ghc-parmake could clean intermediate files that
 aren't mentioned in the makefile itself.

 As for ghc, it's a bit of a slippery slope argument but I don't know that
 it's worth complicating batch-mode compilation for this.  Especially if
 even checking that the source file exists is non-trivial.  As SPJ
 suggests, with each step it gets closer to the functionality already
 present in ```--make```.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8029#comment:5>
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